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392 CHAPTER 9 PROJECT SCHEDULING: PERT/CPM

Summary
In this chapter we have introduced techniques for managing projects:

l Developing a project network diagram is an effective way of planning and managing complex
projects.
l The diagram is used to show the sequencing and inter-connection between the various project
activities.
l By calculating start and finish times we can determine the critical path for the project showing the
minimum completion time. The diagram also identifies activities where there is slack time.
l We can incorporate uncertain or variable activity times and calculate the probability that the project is
completed by a certain time.
l We can also undertake crashing to assess the cost and feasibility of reducing the project
completion time.

WORKED EXAMPLE

he Kellerwirt Gasthaus in Austria is a small, family-run hotel catering for tourists. The hotel is planning to
T replace its small swimming pool with a heated outdoor pool. However, it is critical that the project is
completed in time for the start of the coming summer season, otherwise the hotel risks upsetting guests
expecting to use the new facilities and also risks construction work causing noise and disruption. The summer
season starts in nine weeks’ time. The local company contracted to build the pool have provided the following
information and also indicated that they work five days each week.

Likely Best case Worst case
Preceding duration duration duration
Activity activities (days) (days) (days)
A Remove existing pool - 5 3 6
B Transport rubble off site A 4 2 6
C Excavate new site B 6 5 7
D Install new pool C 9 7 10
E Install solar heating system C 4 2 6
F Test pool for heating and D, E 2 1 3
leakage
G Construction and tiling around D 8 5 10
pool area
H Plant shrubbery around pool G 8 6 10
I Final clean up F, H 4 3 5

What advice can we give the hotel?
First we can calculate the Expected duration times and the variances:

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